Masteries

Offense:
9

Defense:
0

Utility:
21

Honestly, I don't know how to place Lux in a category, she has massively long cooldowns with not so great effects and as a support, her W blocks like 200 damage at level 18, so this is an offensive, mage-ish Lux guide. [As of 10/25/10] This is also my second guide, with my first being Garen which can be found here
PS: If I seem melancholy, downtrodden or outright negative in this build compared to my other guide, I don't know why, just is that way I guess :o

Table of Contents
1. Skills
2. Skill Order and Rotation
3. Masteries
4. Runes
5. Items
6. How and Where Do I Lane?
7. Conclusion

1. Skills
Illumination
Lux's damaging spells charge the target with energy for 6 seconds. Lux's next attack ignites the energy, dealing 20-190 (depending Lux's level) magic damage to the target.
Notes: Basically forces you to auto-attack a champion after hitting a spell, although it's very useful in the beginning and later when you get your Lich Bane

Light Binding
Lux releases a sphere of light that binds and deals damage to up to two enemy units, dealing 50% effect to the 2nd unit struck.
Notes: Useful to protect yourself or get an early kill in the beginning, also helps to run away and kill people late game.

Prismatic Barrier
Lux throws her wand and bends the light around any friendly target it touches, protecting them from enemy damage.
Notes: Pretty useless, spam it in teamfights to protect your teammates from like 200 damage or use it to counteract poisons, ignites etc.

Lucent Singularity
Fires an anomaly of twisted light to an area, which slows nearby enemies. Lux can detonate it to damage enemies in the area of effect.
Notes: An okay slow, also great for farming creep waves or getting your passive on a champion to hit them again. This spell can also be used like a temporary ward, as it gives vision in the spot it is cast to, much like Ashe's bird throw thing that explodes into sparkles.

Finales Funkeln
After gathering energy, Lux fires a beam of light that deals damage to all targets in the area.
Notes: Short cooldown, decent damage, should be used to finish squishies or really low HP tanks.

2. Skill Order and Rotation
R > E > Q > W
Laser > AoE > Bind > Shield
Notes: There is a change though, in the beginning pick up a binding to help prevent yourself from dying or to snare someone for a kill. Other then that, above skill order works for the game.

Combat Rotation
1. Bind with Q
2. Auto attack if possible, or cast E
2a. If auto attacked, blow your E up on them
3. If no auto attack passed, try to make the best of your Lich Bane Proc on something
4. Blow E up
5. Try for another auto attack
6. Wait for cooldowns, auto attack whoever or shield teammates
7. Shoot R when you see a low person
Notes: It's less of a set rotation and more of a reaction as to what is happening, you always want to use your passive and Lich Bane proc for extra damage if possible to feel like you're contributing to team DPS.

Retreating
1. Slow with E
2. Try to snare chasers with Q
3. Shield if possible
4. Hope for the best

3. Masteries
Standard caster build. If this needs more explanation, I'll wait for the comments to ask for some.

4. Runes
Ability power/level, Lux could use cooldown reduction, but her cooldowns are so long, even with the Frozen Heart that extra AP might as well make your cooldowns worth it. Magic penetration is there simply because extra damage never hurts.

5. Items
These items and when you're backing are idealized and may not fit the flow of the game that you're in, it may take some understanding of the game you're in to effectively change some items for more survivability, damage, resists etc.

Start: Always start with the Sapphire Crystal and 2x Health Potions, gives you sufficient mana and health regen to lane until you can at least get your Catalyst.
First Trip Back: Grab your Catalyst, a green ward (or two if you're mid) and boots if possible.
Second Trip Back: Buy your boots of swiftness for extra survivability as a slow Lux is a dead Lux.
Third Trip Back: Finish your Rod of Ages or get a Blasting Wand.

From here on out, it depends on how you're doing in your game and how the flow of the game is going. From this point out, I'll just describe item purchases and why.

Soulstealer: You will always get assists, which basically give you free AP on this item. Although I never get 20 stacks on this item, if you do, the extra cooldown reduction never hurts.
Sheen --> Lich Bane: Your cooldowns are pathetically long, these items help your normal attacks do 500 damage in addition to your spells so you can contribute to team DPS or down a tower.
Frozen Heart: Mostly for survivability, ability spam and cooldown reduction, works awesome with a 20 stack soulstealer but by itself provides mana and armor for a little bit more utility in you.
Zhonya's Ring: +AP, never hurts. Plus you can use it to protect your weak self for 2 seconds and hopefully somebody saves you.

6. How and Where Do I Lane?
I've never been mid as Lux because the side lanes work perfectly fine for me as they're smaller and restrict mobility. This mobility restriction works both ways, which makes wards key for you to stay alive. If you're at mid, place wards on both side bushes, but if you're in a side land, put it in the small river bush nearest you so that way they can't jump out and murder you.

7. Conclusion
In conclusion, I think Lux needs some more brushing up on (I'm getting flame for this, but hey, it's my guide :o) as either a support character or a mage. She also requires a lot of awareness and movement, and if you can't land skillshots, Lux will be challenging for you as all her skills are skillshots. She provides small boosts end game, but mostly just takes up space due to her massively long cooldowns. If you disagree or see changes that need making, or I need to fix some grammar/spelling, leave it in the comments and I'll make sure to get to you.